1. Technical Field
This disclosure relates to a film forming apparatus which forms a coating film by applying a coating material to an outer circumferential surface of a cylindrical object which is formed in an endless belt form. More particularly, the disclosure relates to a film forming apparatus appropriately used for forming an elastic layer of a fixing member such as a fixing roller, a fixing belt, or the like, which fixes an unfixed toner image on a transfer paper by heating and pressurizing the toner image in an image forming apparatus employing an electronic photographic system such as a PPC (a plain paper copier), an LBP (a laser beam printer), a facsimile, or the like.
2. Description of the Related Art
An image forming apparatus such as a copying machine, a printer, or the like, which are based on the principle of electro-photography, performs a fixing process in which a transfer paper is pressed and toner is melted by heat to be fixed on the transfer paper. Recently, in order to improve image grain, an elastic layer, which is made of heat-resistant rubber such as silicon rubber and is formed at a thickness of 100 to 300 μm is formed on a fixing member such as a fixing roller or a fixing belt used in the fixing process so that the fixing member presses the transfer paper with even pressure. The elastic layer is required to have even thickness because variation of the thickness of the elastic layer affects the fixed image and a setup time (time until a predetermined temperature is reached) of the fixing member (fixing roller) based on variation of thermal conductivity of the silicon rubber.
The above-described fixing roller or fixing belt is obtained for example as follows. A primer (an adhesive) is applied on a substrate as an object to be coated (a cylindrical cored bar made of metal such as aluminum or iron, or a belt-shaped substrate made of polyimide, Ni, or the like) and a coating material including heat-resistant rubber such as silicon rubber is applied to form an elastic layer having approximately a thickness of 100 to 300 μm. Then, as mentioned above, the fixing roller or fixing belt can be obtained.
In order to form the above-described elastic layer, various kinds of film forming apparatuses, for example, in a spray coating system or a dipping system where the thickness of the elastic layer as the coating film is controlled by changing viscosity of the coating material are used. In order to change the viscosity of the coating material, the coating material is required to be diluted with solvent. Accordingly, it is not preferable to use the above-described film forming apparatus because use of the solvent cause environmental loads.
Furthermore, the Applicant of the present invention has proposed a film forming apparatus which forms the coating film without diluting the coating material with the solvent, for example a film forming apparatus using a ring coating method (see for example, Japanese Patent Publication No. 2007-14879). The film forming apparatus disclosed in Japanese Patent Publication No. 2007-14879 forms the coating film as follows. The substrate is positioned in a state where an axis of the substrate is disposed parallel to a vertical direction, the substrate is inserted in an annular nozzle unit, and the coating material is applied from an inner circumferential surface of the nozzle unit to an outer circumferential surface of the substrate while the nozzle unit is moved along the axis of the substrate. By use of this type of the film forming apparatus, since only an amount of the coating material to be attached to the substrate is needed, the coating material is not required to be diluted with the solvent.
However, in the film forming apparatus disclosed in Japanese Patent Publication No, 2007-14879, if the substrate is made of polyimide and formed in an endless-belt form, the substrate as the object to be coated is required to be held in an accurately perfect circular form and an interval between the inner circumferential surface of the nozzle unit and the outer circumferential surface of the substrate is required to be maintained constant.
In the film forming apparatus disclosed in Japanese Patent Publication No. 2007-14879, a mandrel as an object supporting device is fitted in the substrate or holds the substrate in a static pressure system. However, desirable accuracy is not achieved by use of the film forming apparatus disclosed in Japanese Patent Publication No. 2007-14879 and in order to form the thin elastic layer at an even thickness, it is necessary to hold the substrate in a more accurately perfect circular form. That is to say, it is difficult to form the elastic layer having even thickness by the above-described film forming apparatus.
On the other hand, it is necessary that an applied pressure of the coating material from the nozzle unit be accurately maintained constant as well as the inner circumferential surface of the nozzle unit being accurately positioned with respect to the outer circumferential surface of the substrate. For example, when the film forming apparatus forms the elastic layer of a thickness approximately between a few μm and 30 μm, the interval between the outer circumferential surface of the substrate and the inner circumferential surface of the nozzle unit must be maintained constant even if the nozzle unit is positioned at any positions in a direction of the axis of the mandrel.